The subject matter involved herein is broadly classified in class 156, subclass 210. Representative prior art is exemplified by U.S. Pat. No. 3,607,523.
For many years, the platens of a double facer were heated by steam. Steam heat has certain disadvantages such as structural considerations due to the high pressure of steam when steam is at the temperature used in a double facer machine. Each steam heated platen is a potential source of danger when in operation due to the high pressure and the compressed state of the steam. Further, there is a limit to the practical upper temperature range for steam and hence a practical upper temperature for heat to be transferred to a web which in turn is a limiting factor on the speed of the web.
The liquid heated platen for use in a double facer in accordance with the present invention is constructed in a manner so as to have a flat planar top surface on a main plate for transferring heat to a web in contact therewith. The main plate is connected to a lower plate therebelow with a peripheral spacer therebetween and sealed to said plates to thereby define a shallow heating chamber between said plates. The chamber is provided with an inlet and an outlet. The chamber inlet is preferably closer to an upstream portion of said plates as compared with said outlet.
The liquid heated platen of the present invention is rigid as a result of beam means connected to the lower plate for maintaining the plates flat and rigid. A means is provided in the chamber to divide the chamber into a labyrinthine flow passage which decreases in cross-sectional area from said inlet to said outlet.
The liquid heated platen of the present invention will enable the double facer machine to be operated at a speed up to 30% greater than the speed of a double facer using steam heated platens. When using a liquid heating medium, such as oil, the vapor pressure is only about 2 psi at 450.degree. F. and a pump is used for circulation. Whereas, with steam the temperature and pressure increase simultaneously at different rates. For example, oil can have a temperature of 450.degree. F. at a pump pressure of 50 psi while steam at the same temperature will result in pressures in excess of 400 psi.
It is an object of the present invention to provide a liquid heated platen for a double facer to facilitate attainment of higher temperatures with lower pressures as compared with steam and various advantages resulting therefrom such as savings in installation, savings in maintenance, etc.
Other objects appear hereinafter.
For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.